The soldering of printed circuit board has been often performed in recent years by a flow soldering. For the flow soldering, an automatic soldering apparatus has been utilized. This automatic soldering apparatus flows molten solder out of a solder bath containing the molten solder through a jet nozzle to solder the printed circuit board. The reasons for soldering the printed circuit board by the flow soldering are that costs in equipment is relatively small even in addition of any peripheral equipment, that this has a high reliability of soldering, and that any components therefor are easily available because the components with leads can be easily manufactured and the like, so that the flow soldering has occupied a major position in the soldering method.
Since, in recent years, requirement for small sized electronic components has been increasing based on popularization of cellular phone or the like, the soldering method is shifted to a reflow soldering which is suitable for soldering the small sized surface mount device. The reflow soldering method is performed so that solder paste and solder ball are formed on a printed circuit board at predetermined positions (electrodes and the like) and the surface mount devices and the like are mounted on the printed circuit board. The soldering is performed by passing such a printed circuit board through a reflow furnace heated at temperature of 220° C. through 250° C. during more than one minute. For this reason, the surface mount device to be soldered on the printed circuit board by the reflow soldering requires a heat-resistant property compared with conventional electronic components by the flow soldering. In recent years, in order to make provision for environmental affairs, the solder used for the flow or reflow soldering has been replaced lead-free solder, melding temperature of which is about 220° C., such as Sn-3.0Ag-0.5Cu with conventional Sn—Pb solder, melding temperature of which is 183° C., which requires any electronic components having a higher heat-resistant property.
Thus, although the soldering method has been shifted from the flow soldering to the reflow soldering and the solder has been replaced the lead-free solder with Sn—Pb solder, most of the electronic components, which has not any heat-resistant property that is required for the reflow soldering and the lead-free solder, for example, such as a precision semiconductor like MPU or the like, connection components, an exterior of which is made of resin, like a connector, a switch or the like, an aluminum electrolytic capacitor which contains electrolyte therein, and the like has been even now retrofitted by manual soldering in which a worker does it using a soldering iron or the like.
Any correction operations of the flow soldering and the reflow soldering by manual soldering by the soldering iron using rosin-core solder are decreased as a result of development of a high performance soldering apparatus based on the advance of technology on the flow soldering and the reflow soldering, but are also often used even now. This manual soldering, however, has reduced an efficiency of work because a person does so and has been subject to a variation of quality because the quality of solder varies based on experience and skill in a worker and it is not easy to train a worker for an experienced and skillful one.
As automation of the manual soldering, a soldering robot or the like has been developed. This, however, has merely replaced the soldering robot with a worker who does the manual soldering by the soldering iron, the soldering robot increasing an efficiency of work but decreasing the efficiency of work compared with the flow or reflow soldering, and too many soldering robots are required for soldering a lot of printed circuit boards, which causes the costs to be increased. Further, a soldering apparatus that applies heat by laser, light beam or the like instead of an application of heat by the soldering iron of the soldering robot has been developed but heat must be rapidly applied to increase the efficiency of work, in which flux contained in the rosin-core solder is subject to any spatter, thereby simply causing poor functioning such as poor conduction, poor insulation or the like.
An invention relating to a point flow soldering apparatus which is replaced with the manual soldering using the soldering iron is disclosed in each of the patent documents 1 and 2. Both of the point flow soldering apparatuses are ones which always flows out a small amount of molten solder to an outside through a small sized nozzle outlet of the jet nozzle for point flow and collects the molten solder thus flown from an outlet arranged around the jet nozzle. Such point flow soldering apparatuses have a problem such that an amount of the solder flown to the outside is small so that the solder is subject to oxidation and oxide generated in the molten solder which has been flown to the outside becomes hard in the small sized nozzle outlet of the jet nozzle so as to be easily stuffed therein.
Accordingly, in the patent document 1, a soldering apparatus has been disclosed in which a periphery of the jet nozzle is set so as to be in an atmosphere of nitrogen, a cover for restraining the molten solder from being oxidized is positioned around the jet nozzle and a spiral pathway is provided between the cover and the jet nozzle. Specifically, this point flow soldering apparatus has a configuration such that the spiral pathway is formed outside the jet nozzle, the jet nozzle is enclosed by a jacket which is able to provide the atmosphere of nitrogen and a whole space between the jet nozzle and the jacket is filled with the nitrogen in order to restrain the molten solder flown out of the jet nozzle from becoming oxide within the spiral pathway and becoming hard.
On the other hand, in the patent document 2, a soldering apparatus has been disclosed in which a cover for allowing a periphery of the jet nozzle to be in an atmosphere of nitrogen is arranged around the jet nozzle and the solder flown out of the jet nozzle is passed between the cover and the jet nozzle. Specifically, a solder collection portion is provided at a forward end of the jet nozzle, the solder collection portion being wider than a solder pathway and being provided at the forward end of the jet nozzle, and a set amount of the solder collected in the solder collection portion is spouted by a gear pump. For this soldering apparatus, it is necessary to put the nozzle outlet of the jet nozzle in an inert atmosphere of nitrogen or the like because a small amount of molten solder spatters and is subject to oxidation.
Thus, the patent documents 1 and 2 both relate to prevention of oxidation of the molten solder flown from the jet nozzle to outside by providing a cover around the outlet of the jet nozzle and filling the periphery of the jet nozzle with an inert gas such as nitrogen gas to intercept oxygen.